This invention relates to circuitry for detecting errors, and more particularly, to circuitry for detecting errors in transceivers of a communication network.
Modules which are coupled to a network generally utilized a driver/receiver pair (a transceiver) to interface with the network. For a network (or link) utilizing a balanced transmission line configuration, the transceiver is a differential pair (differential driver) having A+ and A- terminals. For a balanced transmission line utilizing EIA Standard RS-485, digital signals on the A+ terminal swing between +V volts and 0 volts, while the A- terminal will have digital signals which swing between 0 volts and +V volts, respectively, in a manner well known to those skilled in the art. When an error occurs in one of the drivers, an error mode exists whereby one of the output terminal is stuck at approximately V/2 volts while the other terminal is going through a normal swing between 0 volts and V volts. The net result at the receiver is that of a valid signal. The transmission continues but is unreliable and susceptible to noise thereby reducing the reliability of the transmission and of the system.
Thus there is a need to be able to test the driver (transmitting driver) to verify proper operation of the driver and thus to insure valid communications between modules connected to a network.